A conventionally known muffler has a shell provided by forming metallic half bodies by performing deep-drawing press molding on metallic plates and welding these metallic half bodies. As an example, the muffler of patent literature 1 has a shell provided by forming flared parts at respective opening end portions of two closed-end cylinders resulting from deep-drawing press molding on metallic plates, forming a reverse-tapered opening part having a tip tapered so as to extend outwardly by press molding at the flared part of one of the closed-end cylindrical bodies, forming a forward-tapered opening part having a tip tapered so as to become narrower toward the inside by press molding at the flared part of the other closed-end cylinder, inserting the flared part with the forward-tapered opening part into the flared part with the reverse-tapered opening part so as to make a fit therebetween, and laser welding overlapping parts.
This shell has the flared parts formed by press molding at the respective opening end portions of the two closed-end cylinders. This increases dimension accuracy of the parts fitting into each other. Further, the flared part with the forward-tapered opening part is inserted into the flared part with the reverse-tapered opening part so as to make a fit therebetween. This minimizes a gap between the parts when fitted into each other to ensure a connection formed by laser welding.
A muffler of patent literature 2 has a shell provided by forming a flared part by expanding an opening end portion in diameter of one of two closed-end cylinders resulting from deep-drawing press molding on metallic plates, forming a flange at an opening end portion of the other closed-end cylinder while applying wrinkle holding force and then reducing this opening end portion in diameter so as to remove a residual wrinkle, inserting the opening end portion of the other closed-end cylinder reduced in diameter into the flared part of the former closed-end cylinder so as to make a fit therebetween, and laser welding the overlapping parts.
According to the muffler of patent literature 2, the opening end portion of the other closed-end cylinder is reduced in diameter. This allows the opening end portion of the other closed-end cylinder to be inserted easily into the flared part of the former closed-end cylinder while eliminating a wrinkle from the opening end portion of the other closed-end cylinder. As a result, a gap between the parts fitting into each other is minimized to ensure a connection formed by laser welding.